Finally, I completed this challenge after about 300 tries it seems. TCS 1 ABS 1, and I've been using the DS3 because my wheel is stuck in a cupboard behind Christmas presents lol.
I had to keep going back to it in bytesized sessions to stop getting annoyed. It is so annoying to feel you are doing well but then be disqualified for someone else hitting your car.
But, the reason i persevered was because I know that these challenges are all about learning the course, the braking points the best line through trial and error.
I made many mistakes at Wilson, but had awesome fun, sometimes drifting around the outside of the silver car. I found the best way was if you brake on the outside and get your line right you can move into the apex inside the silver car, and if the grip is there power on at a good pace.
Carefully thread your way through to line up for Chicago, for me this is the key corner. Get on the brakes early to hold the inside line around the tyre-wall, and get straight as early as possible, this allows you to be in 7th place, drafting close all the way up to Hammerhead. Sometimes you can ride the inside of the 8th place car to get the car flat (cheeky).
Hammerhead, as has been said before, can gain you 3 positions. Brake hard and straight on the ouside at the 50m marker, turn in left before getting to close to the cones, switch the weight of the car to the right and try be sensitive with the throttle to get the power down. You should be able to take 5th (or even 4th?) position by gently riding the inside of the other car as he sweeps right.
I had real trouble losing time at follow through, I still never quite got it. I believe if i had mastered it the challenge would be a lot easier. If I do it right then you can take 4th place after the tyre-wall. Out-brake and outmaneuver the metalic blue car through Bacharach and Gambon, and that should leave you with the last lap to over-take the last two cars.
As long as you dont lose your cool (and i almost did at Wilson - took out a few cones on the outside drift) you can take 2nd place at Chicago, and then have your pick of the remaining corners to take 1st, depending on how close you are.
This is a very satisfying challenge to complete, but sooooo ****ing annoying!!!
, i not meaning to show off here but it was quite easy. i found what helped me out the most is completing the sambi bus challenge and finding the best places to brake and accelerate but i like the way the lotus drives it fits my driving style so maybe thats why. ive saved the reply so if anyone wants me to ill upload it to youtube so hopefully some people will also find it easyier to complete 
